There should be and, in the best of cases, there is a synergy between basic research and medical care. In hemophilia care, this synergy has been quite strong and basic research has led to advances (immunopurified replacement products, viral inactivation procedures, recombinant products) that have improved patient care. The purpose of this symposium (Hemophilia Care in the 21st Century, April 8-10, 1999, at the University of North Carolina at Chapel Hill) is to further this synergy by bringing together basic researchers and clinicians to discuss emerging concepts from basic research that may impact hemophilia care. This symposium will specifically examine four areas of emerging research. One is the way that the infectious agent called prions might pose a danger for replacement products. Another area of discussion will be alternatives to conventional replacement therapy, such as using recombinant replacement products that have their activity enhanced by molecular biology techniques or by using viral vectors for gene therapy. This symposium will also discuss some of what is currently known about basic mechanisms for development of inhibitors. This discussion will focus on emerging concepts of T-cell and B-cell interaction as well as the role of antigen presenting cells in inhibitor development. It is anticipated that novel proposals for blocking inhibitor development will be discussed at this symposium. Finally, this symposium will examine unexplained aspects of hemophilia and hemostasis (including thrombotic manifestations in afibrinogenemia patients and sporadic bleeding in factor XI deficient patients). This session will hopefully provide a spur to basic researchers who can attack problems that are of ongoing concern to physicians.